The increasing prevalence of childhood obesity in recent decades has raised serious concerns over impaired physical health, psychosocial maladjustment, and higher mortality rates. Despite growing concerns, substance use, a serious health-risk behavior, has not been largely studied in conjunction with obesity. The proposed project is a prospective longitudinal study that examines relations between adolescent obesity and substance use in young adulthood, and attempts to identify the underlying pathways and processes by which obesity may increase risk for substance use. Taking a biopsychosocial perspective on risk-taking, the proposed study will utilize the sample derived from Waves 1-3 of The National Longitudinal Study of Adolescent Health (Add Health). Data have been obtained on body mass index (BMI) and obesity status; social standing (victimization, peer rejection, feelings of social stigmatization); deviant peer affiliation; psychosocial maladjustment (depressive symptoms) and substance use (alcohol, tobacco, and marijuana) on 11,083 adolescents between 11- 19 years at Wave 1 and 18-26 years at Wave 3. The overarching goal of this research is to determine whether poor social status, deviant peer affiliation and/or psychosocial maladjustment among obese adolescents increase risk of more frequent and severe substance use in young adulthood. Furthermore, ethnic and gender disparities in obesity prevalence and ethnic- and gender-specific associations between body size and social status may influence engagement in substance use. The study's specific aims are to (1) identify whether BMI percentile of obese and non-obese adolescents predicts frequency, severity, and type of substance use in young adulthood; (2) assess whether heterogeneity in social status, deviant peer affiliation, and psychosocial maladjustment among obese adolescents informs the role of adolescent obesity on more frequent and severe substance use in young adulthood; and (3) identify ethnic and gender differences from the above aims to determine whether belonging to groups with higher BMI and obesity rates decreases risk of substance use engagement. As both obesity and substance use are severe burdens on the health care system, identifying the pathways by which adolescent obesity is related to substance use in young adulthood may have significant implications for prevention and intervention efforts aimed at mitigating frequency and severity of substance use. PUBLIC HEALTH RELEVANCE: This study will address two critical public health problems, adolescent obesity and substance use in young adulthood, with the aim of identifying the pathways and processes by which adolescent obesity may increase risk of more frequent and severe substance use in young adulthood, thus informing prevention and intervention efforts for mitigating problematic substance use among young adults. Using The National Longitudinal Study of Adolescent Health (Add Health), the project will evaluate the utility of adolescent social status, deviant peer affiliation, and psychosocial maladjustment as explanatory mechanisms of co-occurring adolescent obesity and substance use in young adulthood. Identifying specific pathways and processes by which obesity and substance use are linked will discern which subgroup(s) of obese adolescents are at highest risk for more frequent and severe substance use in young adulthood, potentially leading to improved efforts in targeting individuals at most need for substance use prevention and intervention services.